Communication control apparatus, communication control method, and computer-readable non-transitory recording medium

ABSTRACT

A communication control apparatus is provided for controlling recovery of data loss during data communication from a first communication device to a second communication device, which includes an obtaining section configured to obtain a temporal change in a communication load between the first communication device and the second communication device. The communication control apparatus also includes a change section configured to dynamically change a permitted time and an interval between transmissions on the basis of the temporal change in the communication load, the permitted time being a time that is permitted to be used by the second communication device for recovery of data loss and the interval between transmissions being an interval between transmissions of a retransmission request message. The communication control apparatus further includes a retransmission control section configured to control transmission of the retransmission request message in accordance with the interval between transmissions.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is divisional of U.S. application Ser. No. 14/474,920filed Sep. 2, 2014, which claims priority to Japanese Application No.2013-187981 filed Sep. 11, 2013. The disclosure of these documents,including the specifications, drawings, and claims, are incorporatedherein by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present disclosure relates to a communication control apparatus, acommunication control method, and a computer-readable non-transitoryrecording medium with which recovery of data lost in the middle of acommunication path is controlled.

2. Description of the Related Art

In order to recover data loss during data communication, aretransmission request message, which is a message that requestsretransmission of a packet identical to a lost packet, is transmittedfrom a reception device to a transmission device, for example. Thetransmission device that has received the retransmission request messageretransmits the packet identical to the lost packet to thereby recoverpacket loss (data loss).

However, data loss may not be appropriately recovered depending on thecommunication status.

SUMMARY OF THE INVENTION

One non-limiting and exemplary embodiment provides a communicationcontrol apparatus that is able to appropriately recover data loss duringdata communication.

Additional benefits and advantages of the disclosed embodiments will beapparent from the specification and figures. The benefits and/oradvantages may be individually provided by the various embodiments andfeatures of the specification and drawings disclosure, and need not allbe provided in order to obtain one or more of the same.

In one general aspect, the techniques disclosed here feature: acommunication control apparatus that includes a first obtaining section,a second obtaining section, and a control section. The first obtainingsection is configured to obtain a first communication status indicatinga frequency of occurrence of data loss during first data communicationfrom a first communication device to a second communication device. Thesecond obtaining section is configured to obtain a second communicationstatus indicating a frequency of occurrence of data loss during seconddata communication from the second communication device to the firstcommunication device. The control section is configured to controltransmission processing relating to transmission from the secondcommunication device to the first communication device in accordancewith the first communication status and the second communication status.The transmission processing includes transmission processing oftransmitting a retransmission request message that requestsretransmission of data identical to lost data during the first datacommunication.

Note that general and specific aspects including the above-describedaspect may be implemented in a form of a system, a method, an integratedcircuit, a computer program, or a computer-readable recording medium,such as a compact disk read-only memory (CD-ROM), or may be implementedusing any combination of a system, a method, an integrated circuit, acomputer program, and a recording medium.

The communication control apparatus according to the present disclosureis able to appropriately recover data loss during data communication.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a diagram for describing data loss during data communication.

FIG. 1B is a diagram for describing automatic retransmission request(ARQ).

FIG. 1C is a diagram for describing ARQ.

FIG. 2A is a diagram for describing retransmission of data identical tolost data.

FIG. 2B is a diagram for describing retransmission of data identical tolost data.

FIG. 2C is a diagram for describing a plurality of times ofretransmission of data identical to lost data.

FIG. 3A is a diagram for describing data loss in the case where the lossrate of a network in the upstream direction is approximately 0%.

FIG. 3B is a diagram for describing data loss in the case where the lossrate of a network in the upstream direction is 1%.

FIG. 3C is a diagram for describing data loss in the case where the lossrate of a network in the upstream direction is 3%.

FIG. 4 is a diagram of a configuration of a communication systemaccording to a first embodiment.

FIG. 5 is a block diagram illustrating a configuration of acommunication control apparatus according to the first embodiment.

FIG. 6 is a flowchart illustrating processing operations performed by areception device according to the first embodiment.

FIG. 7 is a flowchart illustrating processing operations performed bythe communication control apparatus according to the first embodiment.

FIG. 8 is a flowchart illustrating processing operations performed by atransmission device according to the first embodiment.

FIG. 9 is a diagram for describing a specific example of operationsperformed in the communication system according to the first embodiment.

FIG. 10 is a block diagram illustrating a configuration of acommunication control apparatus according to a modified example of thefirst embodiment.

FIG. 11 is a flowchart illustrating processing operations performed bythe communication control apparatus according to the modified example ofthe first embodiment.

FIG. 12 is a diagram for describing a specific example of operationsperformed in a communication system according to the modified example ofthe first embodiment.

FIG. 13A is a diagram illustrating a state where a permittedreproduction time is too long.

FIG. 13B is a diagram illustrating a state where a permittedreproduction time is too short.

FIG. 14 is a diagram illustrating a configuration of a communicationsystem according to a second embodiment.

FIG. 15 is a block diagram illustrating a configuration of acommunication control apparatus according to the second embodiment.

FIG. 16 is a flowchart illustrating processing operations performed by areception device according to the second embodiment.

FIG. 17 is a flowchart illustrating processing operations performed bythe communication control apparatus according to the second embodiment.

FIGS. 18A to 18C are diagrams for describing specific examples ofoperations performed in the communication system according to the secondembodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments will be specifically described with referenceto the drawings, however, needless detailed description may be omitted.For example, detailed description of a well-known matter or duplicateddescription of the substantially same configurations may be omitted inorder to avoid needlessly lengthy description being given below and tofacilitate understanding of those skilled in the art.

Embodiments described hereinafter indicate specific or generic examplesof the present disclosure. The values, shapes, materials, constituentelements, positions and connections of the constituent elements, steps,and orders of the steps indicated in Embodiments are examples, and donot limit the present disclosure. The constituent elements inEmbodiments that are not described in independent Claims that describethe most generic concept of the present disclosure are described asarbitrary constituent elements.

First Embodiment Background Findings

Data loss may occur on a communication path during data communication.For example, as illustrated in FIG. 1A, in the case of transmitting andreceiving video and/or audio data over the Internet, loss of videoand/or audio data (packet loss) may occur. In such a case, images and/orsounds reproduced by a receiver may be distorted. To prevent suchdistortion of images and/or sounds, ARQ has been available.

FIGS. 1B and 1C are diagrams for describing ARQ. In ARQ, a receptiondevice 12 requests a transmission device 11 to retransmit data identicalto lost data (FIG. 1B), and the transmission device 11 retransmits thedata identical to the lost data to the reception device 12 (FIG. 1C).

FIGS. 2A and 2B are diagrams for describing retransmission of dataidentical to lost data. In FIGS. 2A and 2B, data packets respectivelyhaving the sequence numbers “0” to “2” are transmitted, and loss of thedata packet having the sequence number “1” occurs. Then, aretransmission request message that requests retransmission of the datapacket having the sequence number “1” is transmitted from the receptiondevice 12 to the transmission device 11.

Data identical to lost data which is retransmitted in response to theretransmission request message (hereinafter referred to as“retransmission data”) (i) may arrive at the reception device 12 withoutbeing lost (FIG. 2A) or (ii) may be lost again and may not arrive at thereception device 12 (FIG. 2B). Taking into consideration such loss ofretransmission data, it is effective to transmit the retransmission dataa plurality of times until the retransmission data arrives at thereception device 12 as illustrated in FIG. 2C.

However, in the case of transmitting retransmission data a plurality oftimes as described above, it is difficult to appropriately control thenumber of transmission trials. For example, if the number oftransmission trials is too large, extra traffic is generated in thenetwork. On the other hand, if the number of transmission trials is toosmall, failure of data loss recovery may occur. Accordingly, the numberof retransmission trials may be adjusted so as to be appropriate for thereception status of data received from the network.

Japanese Patent No. 3871661 shows that a retransmission request isrepeatedly transmitted at a retransmission request interval determinedon the basis of a buffering time so that the number of repetitions doesnot exceed the maximum number of retransmission trials. Japanese PatentNo. 4699187 shows that the number of transmission trials and theinterval between transmissions of a retransmission request for achievingan inputted permitted loss rate are determined on the basis of the delaytime in a receiver. Japanese Patent No. 5117512 shows that a limitednumber of retransmission trials of each packet is determined on thebasis of a desired reception success probability that is appropriate forthe characteristic of each packet (I packet, P packet, or the like).

However, any of the above-mentioned writings show that the number ofretransmission trials is determined on the basis of the reception statusof data in the network, which is the status of the network in thedownstream direction. The status of the network in the downstreamdirection is the status of the network in a direction in which data (forexample, video data) is received or downloaded from a transmissiondevice to a reception device. Therefore, data loss may not beappropriately recovered depending on the status of the network in theupstream direction, which is the status of the network in a direction inwhich data (for example, a retransmission request message) istransmitted or uploaded to a transmission device. Such a case where dataloss may not be appropriately recovered will be described with referenceto FIGS. 3A to 3C.

FIG. 3A illustrates a case where the loss rate of a network in theupstream direction is approximately 0%. Here, in order to achieve thenumber of retransmission trials, which is “2”, calculated in accordancewith the status of the network in the downstream direction, a receptiondevice transmits two retransmission request messages. In this case, theloss rate of the network in the upstream direction is approximately 0%and therefore substantially no loss of a retransmission request messageoccurs. As a result, in FIG. 3A, all of the two retransmission requestmessages that have been transmitted arrive at a transmission device.Next, the transmission device transmits retransmission data in responseto each of the retransmission request messages that have arrived.Therefore, two pieces of retransmission data are transmitted in total.Of the two pieces of retransmission data, one piece of retransmissiondata is lost in the network and the other piece of retransmission dataeventually arrives at the reception device. As a result, data loss isrecovered in FIG. 3A.

FIG. 3B illustrates a case where the loss rate of a network in theupstream direction is 1%. If the loss rate of a network in the upstreamdirection is high to some extent, loss of a retransmission requestmessage may occur as illustrated in FIG. 3B. As a result, a situation inwhich an actual number of retransmission trials made by a transmissiondevice is less than a number of retransmission trials which is assumedby a reception device may occur. The number of retransmission trialswhich is assumed by the reception device is two in FIG. 3B. The actualnumber of retransmission trials made by the transmission device is onein FIG. 3B. In FIG. 3B, of the two retransmission request messagestransmitted by the reception device, one retransmission request messageis lost and therefore only one piece of retransmission data istransmitted by the transmission device. Then, the retransmission datadoes not arrive at the reception device, because the actual number ofretransmission trials is not appropriate for the loss rate of thenetwork in the downstream direction.

FIG. 3C illustrates a case where the loss rate of a network in theupstream direction is 3%. If the loss rate of a network in the upstreamdirection is higher, an event may occur in which none of theretransmission request messages arrive at a transmission device andretransmission data is not transmitted at all as illustrated in FIG. 3C.

Accordingly, a communication control apparatus according to thisembodiment includes a first obtaining section configured to obtain afirst communication status indicating a frequency of occurrence of dataloss during first data communication from a first communication deviceto a second communication device, a second obtaining section configuredto obtain a second communication status indicating a frequency ofoccurrence of data loss during second data communication from the secondcommunication device to the first communication device, and a controlsection configured to control transmission processing relating totransmission from the second communication device to the firstcommunication device in accordance with the first communication statusand the second communication status. The transmission processingincludes transmission processing of transmitting a retransmissionrequest message that requests retransmission of data identical to lostdata during the first data communication.

According to the configuration described above, transmission processingof transmitting a retransmission request message can be controlled inaccordance with both of the communication statuses, namely, the firstcommunication status of the first data communication from the firstcommunication device to the second communication device and the secondcommunication status of the second data communication from the secondcommunication device to the first communication device. Therefore, evenin the case where the two communication statuses substantially differ,transmission processing of transmitting a retransmission request messagecan be controlled adaptively in accordance with both of the twocommunication statuses, and it becomes possible to appropriately recoverdata loss. For example, it is possible to efficiently recover packetloss relating to video and/or audio data which may occur duringcommunication over the Internet, and the reproduction quality of imagesand/or sounds can be improved.

For example, the control section may include a first determinationsection configured to determine a number of retransmission trials of thedata identical to the lost data to be retransmitted from the firstcommunication device to the second communication device, the number ofretransmission trials being appropriate for the first communicationstatus, a second determination section configured to determine a numberof request trials, which is a number of transmission trials of theretransmission request message to be transmitted from the secondcommunication device to the first communication device, the number ofrequest trials being appropriate for the second communication status,and a retransmission control section configured to control transmissionof the retransmission request message that contains informationspecifying the number of retransmission trials, in accordance with thenumber of request trials.

According to the configuration described above, the number ofretransmission trials of data identical to lost data can be determined,the number of retransmission trials being appropriate for the firstcommunication status, and the number of transmission trials of aretransmission request message (the number of request trials) can bedetermined, the number of transmission trials being appropriate for thesecond communication status. Therefore, the number of retransmissiontrials of data identical to lost data and the number of transmissiontrials of a retransmission request message can be determinedappropriately in accordance with the communication statuses.Furthermore, information specifying the number of retransmission trialsis contained in a retransmission request message and therefore thenumber of retransmission trials can be controlled independently of thenumber of times a retransmission request message arrives at the firstcommunication device. Accordingly, the number of retransmission trialscan be appropriately controlled and it becomes possible to appropriatelyrecover data loss during the data communication.

For example, the first data communication may be packet communication,the first communication status may include a first packet loss rate inthe first data communication, and the first determination section maydetermine the number of retransmission trials such that the number ofretransmission trials becomes larger as the first packet loss rateincreases.

According to the configuration described above, the number ofretransmission trials can be determined in accordance with the packetloss rate, and it becomes possible to appropriately recover packet lossduring the packet communication.

For example, in a case where the number of retransmission trials isdenoted by K1, the first packet loss rate is denoted by LR1, and atarget value of a probability of the retransmitted data identical to thelost data arriving at the second communication device at least once isdenoted by α1, an expression, 1−(LR1)^(K1)≧α1, may be satisfied.

According to the configuration described above, the number ofretransmission trials can be determined so as to satisfy the targetvalue of the probability of retransmitted data identical to lost dataarriving at the second communication device at least once, and itbecomes possible to appropriately recover packet loss during the packetcommunication.

For example, the second data communication may be packet communication,the second communication status may include a second packet loss rate inthe second data communication, and the second determination section maydetermine the number of request trials such that the number of requesttrials becomes larger as the second packet loss rate increases.

According to the configuration described above, the number of requesttrials can be determined in accordance with the packet loss rate, and itbecomes possible to appropriately recover packet loss during the packetcommunication.

For example, in a case where the number of request trials is denoted byK2, the second packet loss rate is denoted by LR2, and a target value ofa probability of the retransmission request message arriving at thefirst communication device at least once is denoted by α2, anexpression, 1−(LR2)^(K2)≧α2, may be satisfied.

According to the configuration described above, the number of requesttrials can be determined so as to satisfy the target value of theprobability of a retransmission request message arriving at the firstcommunication device at least once, and it becomes possible toappropriately recover packet loss during the packet communication.

For example, the control section may determine a number of requesttrials, which is a number of transmission trials of the retransmissionrequest message to be transmitted from the second communication deviceto the first communication device, the number of request trials beingappropriate for the first communication status and the secondcommunication status, and may control transmission of the retransmissionrequest message in accordance with the number of request trials.

According to the configuration described above, the number oftransmission trials of a retransmission request message (the number ofrequest trials) can be determined in accordance with both of the firstcommunication status and the second communication status. That is, thenumber of request trials that is appropriate for both of the firstcommunication status and the second communication status can bedetermined. Therefore, the first communication device can retransmitdata identical to lost data each time a retransmission request messagearrives, and it becomes possible to control the number of retransmissiontrials with a simple configuration.

For example, the control section may include a first determinationsection configured to determine a number of retransmission trials of thedata identical to the lost data to be retransmitted from the firstcommunication device to the second communication device, the number ofretransmission trials being appropriate for the first communicationstatus, and a second determination section configured to determine thenumber of request trials in accordance with the second communicationstatus and the number of retransmission trials so that a number of timesthe retransmission request message arrives at the first communicationdevice is equal to the number of retransmission trials.

According to the configuration described above, the number ofretransmission trials can be determined in accordance with the firstcommunication status, and the number of request trials can be determinedin accordance with the number of retransmission trials and the secondcommunication status.

For example, the second determination section may determine a firstnumber of request trials, which is a number of transmission trialsneeded for the retransmission request message to arrive at the firstcommunication device at least once, in accordance with the secondcommunication status, and may determine a second number of requesttrials, which is the number of request trials, by multiplying the firstnumber of request trials by the number of retransmission trials.

According to the configuration described above, the first number ofrequest trials can be determined in accordance with the secondcommunication status, and the number of transmission trials of aretransmission request message (the second number of request trials) canbe determined by multiplying the first number of request trials by thenumber of retransmission trials.

For example, the second communication status may be measured by using acontrol message that is transmitted from the second communication deviceto the first communication device and that is used to measure the secondcommunication status.

According to the configuration described above, the second communicationstatus is measured by using a control message used to measure the secondcommunication status and therefore it becomes possible to obtain theaccurate second communication status. Accordingly, it becomes possibleto appropriately recover data loss in the data communication.

Note that these general and specific aspects of the present disclosuremay be implemented in a form of a system, a method, an integratedcircuit, a computer program, or a computer-readable recording medium,such as a CD-ROM, or may be implemented using any combination of asystem, a method, an integrated circuit, a computer program, and arecording medium.

Hereinafter, an example of a communication system including acommunication control apparatus according to this embodiment will bespecifically described.

Configuration Configuration of Communication System

FIG. 4 illustrates a configuration of a communication system accordingto the first embodiment. FIG. 4 illustrates a remote display system inwhich video and/or audio data are transmitted and received as an exampleof the communication system. The remote display system includes an inputdevice 100, a transmission device 200, a reception device 300 thatincludes a communication control apparatus 310, and an output device400.

The input device 100 transmits video and/or audio data to thetransmission device 200. The input device 100 is, for example, a digitalvideo camera, a digital still camera, a voice recorder, a smartphone, ora tablet computer.

The transmission device 200 is an example of the first communicationdevice. Specifically, the transmission device 200 is, for example, apersonal computer, a smartphone, a tablet computer, or a communicationadapter. The transmission device 200 transmits video and/or audio datato the reception device 300 over the Internet.

The reception device 300 is an example of the second communicationdevice. Specifically, the reception device 300 is, for example, apersonal computer, a set top box, a disc player or a recorder, or acommunication adapter. The reception device 300 outputs video and/oraudio signals obtained by reproducing video and/or audio data receivedfrom the transmission device 200 to the output device 400.

The output device 400 outputs images, sounds, or both images and soundson the basis of video and/or audio signals. The output device 400 is,for example, a television, a personal computer, a smartphone, or atablet computer.

Hereinafter, data communication from the transmission device 200 to thereception device 300 is called the first data communication. Datacommunication from the reception device 300 to the transmission device200 is called the second data communication.

Next, configurations of the transmission device 200 and the receptiondevice 300 in this embodiment will be described in further detail.

Configuration of Transmission Device

The transmission device 200 includes a transmission section 201, areception section 202, a retransmission control section 203, ameasurement section 204, and a notification section 205.

The transmission section 201 transmits video and/or audio data obtainedfrom the input device 100 to the reception device 300 over the Internet.Specifically, the transmission section 201 first transmits video and/oraudio data (original data). The transmission section 201 transmits videoand/or audio data (retransmission data) according to an instructiongiven by the retransmission control section 203.

The reception section 202 receives a retransmission request message fromthe reception device 300. Then, the reception section 202 communicatesthe retransmission request message to the retransmission control section203. The retransmission request message is a message for the receptiondevice 300 to request retransmission of data identical to lost data.

The reception section 202 communicates information used to measure thesecond communication status to the measurement section 204. The secondcommunication status indicates the frequency of occurrence of data lossduring the second data communication from the reception device 300 tothe transmission device 200. For example, the second communicationstatus may include the packet loss rate in communication of packetizeddata (hereinafter referred to as “packet communication”) from thereception device 300 to the transmission device 200 (hereinafterreferred to as the “second packet loss rate”). In this case, thereception section 202 may communicate the sequence numbers of aplurality of packets received from the reception device 300 to themeasurement section 204 as information used to measure the secondcommunication status.

Note that the reception section 202 may receive a control message (forexample, a message transmitted from the reception device 300 to thetransmission device 200 in order to measure the second communicationstatus), which is different from the retransmission request message. Inthis case, the reception section 202 may communicate the sequencenumbers of a plurality packetized control messages to the measurementsection 204 as information used to measure the second communicationstatus. That is, in this case, the second communication status ismeasured by using control messages. The control messages are transmittedfrom the reception device 300 to the transmission device 200 and used tomeasure the second communication status.

In the case where a retransmission request message has been received,the retransmission control section 203 retransmits, to the receptiondevice 300 via the transmission section 201, data identical to data lost(lost data) during data communication from the transmission device 200to the reception device 300 (first data communication). For example, theretransmission control section 203 retransmits a packet corresponding tothe lost data among a plurality of packets retained in the transmissionsection 201 or a buffer memory (not illustrated).

Note that, in this embodiment, the retransmission control section 203retransmits, to the reception device 300 via the transmission section201, the data identical to the lost data a number of times equal to thenumber of retransmission trials specified by information contained inthe retransmission request message.

The measurement section 204 measures the second communication status.Specifically, the measurement section 204 calculates the number of lostpackets on the basis of the order of the sequence numbers of a pluralityof packets that have arrived from the reception device 300, for example.Then, the measurement section 204 measures the second communicationstatus by using the ratio of the number of lost packets to the totalnumber of packets (the sum of the number of lost packets and the numberof arrived packets) as the second measurement status, for example.Hereinafter, the ratio of the number of lost packets to the total numberof packets is referred to as the “packet loss rate”.

The notification section 205 communicates the second communicationstatus measured by the measurement section 204 to the reception device300. That is, the notification section 205 transmits a messageindicating the second communication status to the reception device 300.

Configuration of Reception Device

The reception device 300 includes a reception section 301, a measurementsection 302, a transmission section 303, and the communication controlapparatus 310.

The reception section 301 receives video and/or audio data from thetransmission device 200. The reception section 301 transmits videoand/or audio signals obtained by reproducing the received video and/oraudio data to the output device 400. For example, the reception section301 generates video and/or audio signals by decoding coded video and/oraudio data and transmits the generated video and/or audio signals to theoutput device 400.

The reception section 301 communicates information used to measure thefirst communication status to the measurement section 302. The firstcommunication status indicates the frequency of occurrence of data lossduring the first data communication from the transmission device 200 tothe reception device 300. For example, in the case where the first datacommunication is packet communication, the first communication statusmay include the packet loss rate in packet communication from thetransmission device 200 to the reception device 300 (hereinafterreferred to as the “first packet loss rate”). In this case, thereception section 301 communicates the sequence numbers of a pluralityof packets received from the transmission device 200 to the measurementsection 302 as information used to measure the first communicationstatus.

The measurement section 302 measures the first communication status.Specifically, the measurement section 302 calculates the number of lostpackets on the basis of the order of the sequence numbers of a pluralityof packets that have arrived from the transmission device 200, forexample. Then, the measurement section 302 measures the firstcommunication status by using the ratio (packet loss rate) of the numberof lost packets to the total number of packets (the sum of the number oflost packets and the number of arrived packets) as the first measurementstatus, for example.

The transmission section 303 transmits a retransmission request messageaccording to an instruction given by the communication control apparatus310. For example, the transmission section 303 transmits aretransmission request message generated by the communication controlapparatus 310. Specifically, the transmission section 303 repeatedlytransmits a retransmission request message at a predetermined regularinterval until the number of repetitions reaches the number of requesttrials, for example. The transmission section 303 may repeatedlytransmit a retransmission request message at a time interval specifiedby the communication control apparatus 310 until the number ofrepetitions reaches the number of request trials, for example.

The transmission section 303 may transmit to the transmission device 200a control message used by the transmission device 200 to measure thesecond communication status. For example, the transmission section 303may repeatedly transmit a control message at a certain time interval.

The communication control apparatus 310 controls recovery of data lossduring the first data communication. Specifically, the communicationcontrol apparatus 310 controls transmission processing of transmitting,from the reception device 300 to the transmission device 200, aretransmission request message that requests retransmission of dataidentical to lost data during the first data communication. Transmissionprocessing of transmitting a retransmission request message isprocessing relating to transmission of a retransmission request message.For example, transmission processing of transmitting a retransmissionrequest message may include processing of determining the content of aretransmission request message or processing of generating aretransmission request message. The detailed configuration of thecommunication control apparatus 310 will be described below.

Configuration of Communication Control Apparatus

FIG. 5 illustrates a configuration of the communication controlapparatus 310 according to the first embodiment. The communicationcontrol apparatus 310 includes a first obtaining section 311, a secondobtaining section 312, and a control section 313.

The first obtaining section 311 obtains the first communication status.In this embodiment, the first obtaining section 311 obtains the firstcommunication status from the measurement section 302 of the receptiondevice 300.

The second obtaining section 312 obtains the second communicationstatus. In this embodiment, the second obtaining section 312 obtains thesecond communication status from the notification section 205 of thetransmission device 200.

The control section 313 controls transmission processing oftransmitting, from the reception device 300 to the transmission device200, a retransmission request message that requests retransmission ofdata identical to lost data during the first data communication, on thebasis of the first communication status obtained by the first obtainingsection 311 and the second communication status obtained by the secondobtaining section 312. In this embodiment, the control section 313controls (i) information to be contained in a retransmission requestmessage and (ii) the number of transmission trials of the retransmissionrequest message.

As illustrated in FIG. 5, the control section 313 includes a firstdetermination section 314, a second determination section 315, and aretransmission control section 316, for example.

The first determination section 314 determines the number ofretransmission trials of data identical to lost data from thetransmission device 200 to the reception device 300, the number ofretransmission trials being appropriate for the first communicationstatus. For example, the first determination section 314 determines thenumber of retransmission trials such that the number of retransmissiontrials becomes larger as the frequency of data loss indicated by thefirst communication status increases. Specifically, in the case wherethe first data communication is packet communication and the firstcommunication status includes the first packet loss rate, for example,the first determination section 314 determines the number ofretransmission trials such that the number of retransmission trialsbecomes larger as the first packet loss rate increases.

The second determination section 315 determines the number of requesttrials, which is the number of transmission trials of a retransmissionrequest message from the reception device 300 to the transmission device200, the number of request trials being appropriate for the secondcommunication status. For example, the second determination section 315determines the number of request trials such that the number of requesttrials becomes larger as the frequency of data loss indicated by thesecond communication status increases. Specifically, in the case wherethe second data communication is packet communication and the secondcommunication status includes the second packet loss rate, for example,the second determination section 315 determines the number of requesttrials such that the number of request trials becomes larger as thesecond packet loss rate increases.

The retransmission control section 316 controls transmission of aretransmission request message to the transmission device 200 inaccordance with the number of request trials determined by the seconddetermination section 315, the retransmission request message containinginformation specifying the number of retransmission trials determined bythe first determination section 314. Here, the retransmission controlsection 316 repeatedly transmits, to the transmission device 200 via thetransmission section 303, a retransmission request message until theretransmitted data identical to the lost data is received, whileassuming that the number of request trials is the upper limit of thenumber of repetitions.

Specifically, the retransmission control section 316 generates aretransmission request message that contains information specifying thenumber of retransmission trials, for example. Then, the retransmissioncontrol section 316 communicates the retransmission request message tothe transmission section 303 in accordance with the number of requesttrials to thereby make the transmission section 303 transmit theretransmission request message.

For example, the retransmission control section 316 may communicate thenumber of request trials and the number of retransmission trials to thetransmission section 303. In this case, the transmission section 303 maygenerate a retransmission request message that contains informationspecifying the number of retransmission trials. Then, the transmissionsection 303 may transmit the retransmission request message to thetransmission device 200 in accordance with the number of request trials.

Operations

Next, operations performed in the communication system configured asdescribed above will be described with reference to the drawings.

Operations Performed by Reception Device

FIG. 6 is a flowchart illustrating processing operations performed bythe reception device 300 according to the first embodiment.

First, the reception section 301 receives video and/or audio data fromthe transmission device 200 (step S101). The measurement section 302measures the first communication status (step S102), and determineswhether or not data loss has occurred (step S103).

If data loss has not occurred (No in step S103), the flow returns tostep S101. For example, in the case where the measurement section 302has not detected loss of video and/or audio data, the measurementsection 302 keeps measuring the first communication status.

On the other hand, if data loss has occurred (Yes in step S103), thecommunication control apparatus 310 controls retransmission of dataidentical to the lost data (step S104), and the flow returns to stepS101. For example, in the case where the measurement section 302 hasdetected loss of video and/or audio data, the communication controlapparatus 310 performs processing for controlling retransmission of dataidentical to the lost data. Operations performed by the communicationcontrol apparatus 310 in step S104 will be described with reference toFIG. 7.

Operations Performed by Communication Control Apparatus

FIG. 7 is a flowchart illustrating processing operations performed bythe communication control apparatus 310 according to the firstembodiment. That is, FIG. 7 illustrates the details of step S104 in FIG.6.

First, the first obtaining section 311 obtains the first communicationstatus (step S201). The obtained first communication status is inputtedto the first determination section 314.

Next, the first determination section 314 determines the number ofretransmission trials of the data identical to the lost data inaccordance with the first communication status (step S202). Thedetermined number of retransmission trials is inputted to theretransmission control section 316.

The second obtaining section 312 obtains the second communication status(step S203). The obtained second communication status is inputted to thesecond determination section 315.

The second determination section 315 determines the number oftransmission trials of a retransmission request message (the number ofrequest trials) in accordance with the second communication status (stepS204). The determined number of request trials is inputted to theretransmission control section 316.

The retransmission control section 316 controls transmission of aretransmission request message containing information specifying thenumber of retransmission trials in accordance with the number of requesttrials (step S205).

Here, a specific example of processing performed in order to determinethe number of retransmission trials in step S202 and to determine thenumber of request trials in step S204 will be described. In the specificexample, both of the first data communication and the second datacommunication are packet communication, and both data identical to lostdata and a retransmission request message are packetized. Hereinafter,packetized data identical to lost data is called a packet identical to alost packet, and a packetized retransmission request message is called aretransmission request packet.

In the specific example, the first communication status includes a firstpacket loss rate LR1. The second communication status includes a secondpacket loss rate LR2.

First, a method of calculating the number of retransmission trials K1needed for a retransmitted packet identical to a lost packet to arriveat the reception device 300 at least once will be described. The firstpacket loss rate LR1 is the probability of loss of a packet when thepacket is transmitted from the transmission device 200 to the receptiondevice 300 once. Therefore, in the case where a packet is transmitted K1times, the probability of loss of the packet in all cases is expressedby (LR1)K1. Accordingly, the first determination section 314 calculatesthe number of retransmission trials K1 so as to satisfy expression (1)below. More specifically, the first determination section 314 calculatesthe minimum value of the number of retransmission trials K1 thatsatisfies expression (1) below. As a result, the number ofretransmission trials K1 needed for a retransmitted packet identical toa lost packet to arrive at the reception device 300 at least once iscalculated.

1−(LR1)^(K1)≧α1  (1)

Here, α1 is a target value of the probability (transmission successrate) of a retransmitted packet identical to a lost packet arriving atthe reception device 300 at least once. α1 may be a predetermined value(for example, “0.999”). Alternatively, α1 may be determined adaptivelyin accordance with the importance of the lost packet.

Next, a method of calculating the number of request trials K2 needed fora retransmission request packet to arrive at the transmission device 200at least once will be described. The second packet loss rate LR2 is theprobability of loss of a packet when the packet is transmitted from thereception device 300 to the transmission device 200 once. Therefore, inthe case where a packet is transmitted K2 times, the probability of lossof the packet in all cases is expressed by (LR2)^(K2). Accordingly, thesecond determination section 315 calculates the number of request trialsK2 so as to satisfy expression (2) below. More specifically, the seconddetermination section 315 calculates the minimum value of the number ofrequest trials K2 that satisfies expression (2) below. As a result, thenumber of request trials K2 needed for a retransmission request packetto arrive at the transmission device 200 at least once is calculated.

1−(LR2)^(K2)≧α2  (2)

Here, α2 is a target value of the probability (transmission successrate) of a retransmission request packet arriving at the transmissiondevice 200 at least once. α2 may be a predetermined value (for example,“0.999”). Alternatively, α2 may be determined adaptively in accordancewith the importance of the lost packet.

Operations Performed by Transmission Device

Next, operations performed by the transmission device 200 in the casewhere a retransmission request message is received will be described.FIG. 8 is a flowchart illustrating processing operations performed bythe transmission device 200 according to the first embodiment.

First, the retransmission control section 203 determines whether or nota retransmission request message has been received (step S301). If aretransmission request message has not been received (No in step S301),determination as to whether or not a retransmission request message hasbeen received is repeatedly performed.

On the other hand, if a retransmission request message has been received(Yes in step S301), the retransmission control section 203 obtains thenumber of retransmission trials from the retransmission request message(step S302). The retransmission control section 203 retransmits dataidentical to lost data specified by the retransmission request message anumber of times equal to the number of retransmission trials (stepS303).

Specific Example of Operations Performed in Communication System

Next, a specific example of operations performed in the communicationsystem according to this embodiment as described above will bedescribed. FIG. 9 is a diagram for describing a specific example ofoperations performed in the communication system according to the firstembodiment.

In FIG. 9, data packets respectively having the sequence numbers “0” to“2” are transmitted and loss of the data packet having the sequencenumber “1” occurs. Then, the communication control apparatus 310 of thereception device 300 determines the number of retransmission trials andthe number of request trials.

Specifically, the first determination section 314 determines the numberof retransmission trials to be “2” in accordance with the first packetloss rate of “1%” in the first data communication. The seconddetermination section 315 determines the number of request trials to be“4” in accordance with the second packet loss rate of “3%” in the seconddata communication. As a result, a retransmission request packet istransmitted four times. The retransmission request packet contains (i)information used to request retransmission of the data packet having thesequence number “1” and (ii) information specifying that the number ofretransmission trials is “2”. The retransmission request packet arrivesat the transmission device 200 only once.

The retransmission control section 203 of the transmission device 200obtains the number of retransmission trials “2” from the retransmissionrequest packet. The retransmission control section 203 transmits thedata packet (lost packet) having the sequence number “1” via thetransmission section 201 twice. As a result, the retransmitted packetidentical to the lost packet arrives at the reception device 300 once.

Effects

As described above, the communication control apparatus 310 according tothis embodiment is able to control transmission processing oftransmitting a retransmission request message in accordance with both ofthe communication statuses, namely, the first communication status ofthe first data communication from the transmission device 200 to thereception device 300 and the second communication status of the seconddata communication from the reception device 300 to the transmissiondevice 200. Therefore, even in the case where the two communicationstatuses substantially differ, transmission processing of transmitting aretransmission request message can be controlled adaptively inaccordance with both of the two communication statuses, and it becomespossible to appropriately recover data loss.

The first determination section 314 is able to determine the number ofretransmission trials of data identical to lost data, the number ofretransmission trials being appropriate for the first communicationstatus, and the second determination section 315 is able to determinethe number of transmission trials of a retransmission request message(the number of request trials), the number of transmission trials beingappropriate for the second communication status. Therefore, thecommunication control apparatus 310 is able to determine the number ofretransmission trials of data identical to lost data and the number oftransmission trials of a retransmission request message appropriately inaccordance with the communication statuses. Furthermore, informationspecifying the number of retransmission trials is contained in aretransmission request message and therefore it becomes possible tocontrol the number of retransmission trials independently of the numberof times a retransmission request message arrives at the transmissiondevice 200. Therefore, the number of retransmission trials can beappropriately controlled, and it becomes possible to appropriatelyrecover data loss during data communication.

Modified Example

Next, a modified example of the first embodiment will be described. Inthis modified example, the method of determining the number of requesttrials is different from that in the first embodiment. Consequently, inthis modified example, a retransmission request message need not containinformation specifying the number of retransmission trials. Note thatdescription of configurations and processing similar to those in thefirst embodiment will be omitted hereinafter.

FIG. 10 illustrates a configuration of a communication control apparatus310 a according to the modified example of the first embodiment. Thecommunication control apparatus 310 a includes the first obtainingsection 311, the second obtaining section 312, and a control section 313a.

The control section 313 a determines the number of transmission trials(the number of request trials) of a retransmission request message to betransmitted from the reception device 300 to the transmission device200, the number of transmission trials being appropriate for the firstcommunication status and the second communication status. The controlsection 313 a controls transmission of a retransmission request messagein accordance with the determined number of request trials. The controlsection 313 a includes the first determination section 314, a seconddetermination section 315 a, and a retransmission control section 316 a.

The first determination section 314 determines the number ofretransmission trials that is appropriate for the first communicationstatus similarly as in the first embodiment.

The second determination section 315 a determines the number of requesttrials in accordance with the second communication status and the numberof retransmission trials so that the number of times a retransmissionrequest message arrives at the transmission device 200 is equal to thenumber of retransmission trials determined by the first determinationsection 314. That is, the second determination section 315 a adjusts thenumber of request trials determined in accordance with the secondcommunication status (without taking into consideration the firstcommunication status) such that the number of request trials becomeslarger as the number of retransmission trials determined by the firstdetermination section 314 increases.

For example, the second determination section 315 a first determines afirst number of request trials, which is the number of transmissiontrials needed for a retransmission request message to arrive at thetransmission device 200 at least once. Subsequently, the seconddetermination section 315 a determines a second number of request trialsby multiplying the determined first number of request trials by thenumber of retransmission trials determined by the first determinationsection 314. The second number of request trials is used for control oftransmission of a retransmission request message.

The retransmission control section 316 a controls transmission of aretransmission request message to the transmission device 200 inaccordance with the second number of request trials determined by thesecond determination section 315 a. This retransmission request messageneed not necessarily contain information specifying the number ofretransmission trials.

Next, operations performed by the communication control apparatus 310 aconfigured as described above will be described. FIG. 11 is a flowchartillustrating processing operations performed by the communicationcontrol apparatus 310 a according to the modified example of the firstembodiment. Specifically, FIG. 11 illustrates the details of step S104 ain FIG. 6.

After processing in steps S201 to S203 has been performed similarly asin FIG. 7, the second determination section 315 a determines the numberof request trials in accordance with the second communication status andthe number of retransmission trials so that the number of times aretransmission request message arrives at the transmission device 200 isequal to the number of retransmission trials determined by the firstdetermination section 314 (step S204 a).

Specifically, the second determination section 315 a determines thefirst number of request trials, which is the number of transmissiontrials needed for a retransmission request message to arrive at thetransmission device 200 at least once (step S2041 a). Subsequently, thesecond determination section 315 a determines the second number ofrequest trials by multiplying the first number of request trialsdetermined in step S2041 a by the number of retransmission trialsdetermined in step S202 (step S2042 a).

The retransmission control section 316 a transmits a retransmissionrequest message to the transmission device 200 via the transmissionsection 303 in accordance with the second number of request trials (stepS205 a).

Next, a specific example of operations performed in the communicationsystem according to this modified example as described above will bedescribed. FIG. 12 is a diagram for describing a specific example ofoperations performed in the communication system according to themodified example of the first embodiment.

In FIG. 12, data packets respectively having the sequence numbers “0” to“2” are transmitted and loss of the data packet having the sequencenumber “1” occurs similarly as in FIG. 9 of the first embodiment.

Then, the first determination section 314 determines the number ofretransmission trials to be “2” in accordance with the first packet lossrate of “1%” similarly as in FIG. 9. The second determination section315 a determines the first number of request trials to be “4” inaccordance with the second packet loss rate of “3%”. Furthermore, thesecond determination section 315 a determines the second number ofrequest trials to be “8” by multiplying the first number of requesttrials “4” by the number of retransmission trials “2”. As a result, aretransmission request packet is transmitted to the transmission device200 eight times, and the retransmission request packet arrives at thetransmission device 200 twice.

The retransmission control section 203 of the transmission device 200retransmits a data packet identical to the lost data packet a number oftimes equal to the number of times the retransmission request packetarrives. As a result, the retransmitted data packet identical to thelost data packet arrives at the reception device 300 once.

As described above, a retransmission request packet arrives at thetransmission device 200 at least a number of times equal to the numberof retransmission trials calculated by the first determination section314. The transmission device 200 transmits a packet identical to thelost packet once each time a retransmission request packet arrives.Accordingly, the packet identical to the lost packet is transmitted atleast a number of times equal to the number of retransmission trialsdetermined by the first determination section 314. As a result, theretransmitted packet identical to the lost packet arrives at thereception device 300 at least once.

As described above, the communication control apparatus 310 a accordingto this modified example is able to determine the number of transmissiontrials of a retransmission request message (the number of requesttrials) in accordance with both of the first communication status andthe second communication status. That is, the communication controlapparatus 310 a is able to determine the number of request trials thatis appropriate for both of the first communication status and the secondcommunication status. Therefore, the transmission device 200 retransmitsdata identical to lost data each time a retransmission request messagearrives, and it becomes possible to control the number of retransmissiontrials with a simple configuration.

Second Embodiment Background Findings

As illustrated in FIGS. 1B and 1C, in ARQ, the reception device 12requests the transmission device 11 to retransmit data identical to lostdata (FIG. 1B), and the transmission device 11 retransmits the dataidentical to the lost data to the reception device 12 (FIG. 1C). In thiscase, when taking into consideration loss of retransmission data, it iseffective to retransmit the data identical to the lost data a pluralityof times until the retransmitted data identical to the lost data arrivesat the reception device 12 as illustrated in FIG. 2C.

In the case of retransmitting data identical to lost data a plurality oftimes, generally, retransmission may be performed a plurality of timeswithin a time period from the time when data loss is detected until theestimated time of reproduction of the data identical to the lost data(hereinafter referred to as a “permitted reproduction time”). Here, ifthe interval between retransmissions for retransmission performed aplurality of times is a regular interval, it is possible to perform alarger number of retransmissions as the permitted reproduction timebecomes longer. If the number of retransmission trials is fixed, it ispossible to make the interval between retransmissions longer as thepermitted reproduction time becomes longer.

Generally, it is possible to increase the probability of success inrecovery of data loss (hereinafter referred to as the “recovery rate”)as the number of retransmission trials increases. It is possible tosuppress a bandwidth shortage caused by retransmission more as theinterval between retransmissions becomes longer. Therefore, a longerpermitted reproduction time is better from the viewpoint of thestability of communication.

However, if the permitted reproduction time is longer, a delay inreproduction may occur, which is a shortcoming. For example, if thepermitted reproduction time becomes longer in a television conferencesystem or the like, it becomes difficult to smoothly have a conversationusing such a system. Therefore, the permitted reproduction time needs tobe set appropriately in accordance with the characteristics of anapplication program (hereinafter referred to as an “application”) whichuses data.

Japanese Patent No. 4699187 shows that the permitted packet loss rate(permitted loss rate) and a permitted amount of time of a reproductiondelay in reproducing packets (permitted reproduction time) arerespectively inputted using input units. Then, the number oftransmission trials and the interval between transmissions of aretransmission request message needed in order to achieve the permittedloss rate within the permitted reproduction time are determined. In thisway, the permitted loss rate and the permitted reproduction time can beinputted in accordance with an application involved, and it is possibleto attain the recovery rate of lost data and the real-time property ofdata reproduction that suit the application.

However, it is difficult to input the permitted reproduction time inadvance as described in Japanese Patent No. 4699187. For example, evenin the case where data is used in the same application, an appropriatepermitted reproduction time may differ depending on the environment (forexample, the processing capacity of a processor or the like) in whichthe data is used. Furthermore, it is not practical to input thepermitted reproduction time each time data is used, in accordance withthe environment in which the data is used because effort made by a userincreases.

Even if data is used in the same application and the environment inwhich the data is used is the same, the communication status (forexample, the network characteristics) dynamically changes in general.

Accordingly, the permitted reproduction time that was set may becomeinappropriate as time passes. That is, in the case where a permittedreproduction time set in advance is used, a situation where thepermitted reproduction time is too long (for example, FIG. 13A) or asituation where the permitted reproduction time is too short (forexample, FIG. 13B) may occur. In the case where the permittedreproduction time is too long as illustrated in FIG. 13A, a delay indata reproduction occurs and the real-time property of data reproductionis degraded. On the other hand, in the case where the permittedreproduction time is too short as illustrated in FIG. 13B, a bandwidthshortage occurs and the frequency of occurrence of data loss isincreased.

Accordingly, a communication control apparatus according to thisembodiment is a communication control apparatus for controlling recoveryof data loss during data communication from a first communication deviceto a second communication device. The communication control apparatusincludes a obtaining section configured to obtain a temporal change in acommunication load between the first communication device and the secondcommunication device, a change section configured to dynamically changea permitted time and an interval between transmissions on the basis ofthe temporal change in the communication load, the permitted time beinga time that is permitted to be used by the second communication devicefor recovery of data loss, the interval between transmissions being aninterval between transmissions of a retransmission request message thatrequests retransmission of data identical to lost data in a case wherethe retransmission request message is repeatedly transmitted from thesecond communication device to the first communication device, and aretransmission control section configured to control transmission of theretransmission request message in accordance with the interval betweentransmissions.

According to the configuration described above, the permitted time thatis a time permitted to be used for recovery of data loss and theinterval between transmissions of a retransmission request message canbe dynamically changed in accordance with the communication load.Therefore, it becomes possible to balance suppression of increase inloss due to communication congestion with reduction in a reproductiondelay. For example, it is possible to efficiently recover loss ofpackets of video and/or audio data occurring during communication overthe Internet while suppressing congestion caused by the communicationload. In this case, it is also possible to reduce a reproduction delayin reproducing video and/or audio data, and it is possible to improvethe reproduction quality of images and/or sounds.

For example, the change section may dynamically change the permittedtime on the basis of the temporal change in the communication load, andmay determine the interval between transmissions that is appropriate forthe permitted time so that the retransmitted data identical to the lostdata arrives at the second communication device within the permittedtime in a case where the retransmission request message has beentransmitted a number of times equal to a number of request trials.

According to the configuration described above, it is possible todetermine the interval between transmissions of a retransmission requestmessage so that retransmitted data identical to lost data arrives at thesecond communication device within a permitted time, by dynamicallychanging the permitted time on the basis of the temporal change in thecommunication load.

For example, the change section may increase the permitted time in acase where the communication load is increasing, and may decrease thepermitted time in a case where the communication load is decreasing.

According to the configuration described above, the permitted time canbe changed appropriately in accordance with the increase or decrease ofthe communication load, and it becomes possible to balance suppressionof communication congestion with reduction in a reproduction delay.

For example, the change section may increase the permitted time in acase where a duration during which the communication load keepsincreasing exceeds a first threshold time, and may decrease thepermitted time in a case where a duration during which the communicationload keeps decreasing exceeds a second threshold time.

According to the configuration described above, the permitted time canbe changed on the basis of the result of comparison between the durationduring which the communication load keeps increasing or decreasing andthe threshold. Therefore, it is possible to suppress frequent changes inthe permitted time and the interval between transmissions, and it ispossible to attain stable data reproduction and communication.

For example, the obtaining section may estimate a temporal change in thecommunication load in accordance with at least one of temporal changesin a loss frequency, a delay time, and traffic in the first datacommunication.

According to the configuration described above, a temporal change in thecommunication load can be estimated on the basis of at least one of thetemporal changes in the loss frequency, delay time, and traffic.

For example, the obtaining section may obtain a temporal change in thecommunication load from outside the communication control apparatus.

According to the configuration described above, a temporal change in thecommunication load can be obtained from outside the communicationcontrol apparatus.

Note that these general and specific aspects of the present disclosuremay be implemented in a form of a system, a method, an integratedcircuit, a computer program, or a computer-readable recording medium,such as a CD-ROM, or may be implemented using any combination of asystem, a method, an integrated circuit, a computer program, and arecording medium.

Hereinafter, an example of a communication system including acommunication control apparatus according to this embodiment will bespecifically described. Description of configurations and processingsimilar to those in the first embodiment will be omitted as appropriate.

Configuration Configuration of Communication System

FIG. 14 illustrates a configuration of a communication system accordingto the second embodiment. This communication system (remote displaysystem) includes the input device 100, a transmission device 500, areception device 600 including a communication control apparatus 610,and the output device 400.

The transmission device 500 is an example of the first communicationdevice. The transmission device 500 transmits video and/or audio data tothe reception device 600 over the Internet. The transmission device 500is, for example, a personal computer, a smartphone, a tablet computer,or a communication adapter.

The reception device 600 is an example of the second communicationdevice. The reception device 600 transmits video and/or audio datareceived from the transmission device 500 to the output device 400. Thereception device 600 is, for example, a personal computer, a set topbox, a disc player or a recorder, or a communication adapter.

Next, configurations of the transmission device 500 and the receptiondevice 600 in this embodiment will be described in further detail.

Configuration of Transmission Device

The transmission device 500 includes a transmission section 501, areception section 502, and a retransmission control section 503.

The transmission section 501 transmits video and/or audio data obtainedfrom the input device 100 to the reception device 600 over the Internetsimilarly as in the transmission section 201 of the first embodiment.

The reception section 502 receives a retransmission request message fromthe reception device 600. Then, the reception section 502 communicatesthe retransmission request message to the retransmission control section503.

The retransmission control section 503 retransmits, to the receptiondevice 600 via the transmission section 501, data identical to data lost(lost data) during data communication from the transmission device 500to the reception device 600 (first data communication) once each time aretransmission request message is received. For example, theretransmission control section 503 retransmits a packet corresponding tothe lost data among a plurality of packets retained in the transmissionsection 501 or a buffer memory (not illustrated).

Configuration of Reception Device

The reception device 600 includes a reception section 601, a measurementsection 602, a transmission section 603, and the communication controlapparatus 610.

The reception section 601 receives video and/or audio data from thetransmission device 500 as in the reception section 301 of the firstembodiment. The reception section 601 transmits signals based on thereceived video and/or audio data to the output device 400.

The reception section 601 communicates information used to measure atemporal change in the communication load in the first datacommunication to the measurement section 602. Specifically, thereception section 601 communicates information about packets receivedfrom the transmission device 500 to the measurement section 602, forexample.

The measurement section 602 measures the communication status of thefirst data communication. For example, the measurement section 602measures at least one of the temporal changes in the loss frequency,delay time, and traffic. Specifically, the measurement section 602 maymeasure the loss frequency and delay time in the first datacommunication by using a response packet returned in response to an echorequest message transmitted to the transmission device 500, for example.The measurement section 602 may measure temporal changes in the lossfrequency and delay time by repeatedly performing such measurement.

The transmission section 603 transmits a retransmission request messageaccording to an instruction given by the communication control apparatus610. For example, the transmission section 603 transmits aretransmission request message at an interval between transmissionscalculated by the communication control apparatus 610. Specifically, thetransmission section 603 repeatedly transmits a retransmission requestmessage at an interval between transmissions calculated by thecommunication control apparatus 610 until the number of repetitionsreaches the number of request trials, for example. The transmissionsection 603 may repeatedly transmit a retransmission request message ata time interval specified by the communication control apparatus 610until the number of repetitions reaches the number of request trials,for example.

The communication control apparatus 610 is an apparatus used to recoverdata loss during the first data communication. Specifically, thecommunication control apparatus 610 controls transmission processing oftransmitting a message (retransmission request message) which requestsretransmission of lost data. The communication control apparatus 610communicates a permitted time to the output device 400. The detailedconfiguration of the communication control apparatus 610 will bedescribed below.

Configuration of Communication Control Apparatus

FIG. 15 illustrates a configuration of the communication controlapparatus 610 according to the second embodiment. The communicationcontrol apparatus 610 includes an obtaining section 611, a changesection 612, and a retransmission control section 613.

The obtaining section 611 is an example of the obtaining section. Theobtaining section 611 obtains a temporal change in the communicationload between the transmission device 500 and the reception device 600.Here, the communication load indicates the degree of congestion of pathsused in the first data communication. In other words, the communicationload indicates the degree of shortage of the communication bands betweenthe transmission device 500 and the reception device 600.

Specifically, the obtaining section 611 estimates a temporal change inthe communication load on the basis of at least one of the temporalchanges in the loss frequency, delay time, and traffic in the first datacommunication, the temporal changes having been obtained from themeasurement section 602, for example. The obtaining section 611 mayestimate that the communication load is increasing in the case where theloss frequency, delay time, or traffic is increasing, for example. Onthe other hand, the obtaining section 611 may estimate that thecommunication load is decreasing in the case where the loss frequency,delay time, or traffic is decreasing, for example.

Note that the obtaining section 611 may obtain a temporal change in thecommunication load from outside the communication control apparatus 610.For example, the obtaining section 611 may obtain a temporal change inthe communication load from a monitoring server that monitors thenetwork.

The obtaining section 611 may obtain the number of transmission trialsof a retransmission request message (the number of request trials). Forexample, the obtaining section 611 may determine the number ofretransmission trials of data identical to lost data in accordance withthe first communication status similarly as in the first embodiment, andmay obtain the determined number of retransmission trials as the numberof request trials. Note that the obtaining section 611 may obtain thenumber of request trials from outside the communication controlapparatus 610.

The change section 612 dynamically changes the permitted time and theinterval between transmissions of a retransmission request message onthe basis of the temporal change in the communication load obtained bythe obtaining section 611. The permitted time is a time that ispermitted to be used by the reception device 600 for recovery of dataloss. For example, the permitted time may be the permitted reproductiontime. That is, the permitted time may be a time period from the timewhen data loss is detected until the estimated time of reproduction ofdata identical to the lost data. The interval between transmissions is atime interval at which a retransmission request message is transmittedin the case of repeatedly transmitting the retransmission requestmessage from the reception device 600 to the transmission device 500.

The permitted time may be a time period from the time when data loss isdetected until when data identical to the lost data is received.

Specifically, the change section 612 first dynamically changes thepermitted time on the basis of the temporal change in the communicationload. For example, the change section 612 increases the permitted timewhen the communication load is increasing, and decreases the permittedtime when the communication load is decreasing.

Next, the change section 612 determines the interval betweentransmissions that is appropriate for the permitted time so thatretransmitted data identical to lost data arrives at the receptiondevice 600 within the permitted time in the case where a retransmissionrequest message has been transmitted a number of times equal to thenumber of request trials. For example, the change section 612 determinesthe number of request trials so that the result of multiplying theinterval between transmissions by the number of request trials is equalto or less than the permitted time.

The retransmission control section 613 controls transmission of aretransmission request message in accordance with the interval betweentransmissions changed by the change section 612. That is, theretransmission control section 613 transmits a retransmission requestmessage at the changed interval between transmissions.

Operations

Next, operations performed in the communication system configured asdescribed above will be described with reference to the drawings.

Operations Performed by Reception Device

FIG. 16 is a flowchart illustrating processing operations performed bythe reception device 600 according to the second embodiment. Here, acase where a certain value (for example, an initial value) is set forthe permitted reproduction time will be described.

First, the reception section 601 receives video and/or audio data fromthe transmission device 500 (step S401). The measurement section 602measures the communication status of the first data communication (stepS402), and determines whether or not data loss has occurred (step S403).

Here, if data loss has not occurred (No in step S403), the flow returnsto step S401. That is, in the case where the measurement section 602 hasnot detected loss of video and/or audio data, for example, themeasurement section 602 keeps measuring the communication status of thefirst data communication.

On the other hand, if data loss has occurred (Yes in step S403), thecommunication control apparatus 610 controls retransmission of dataidentical to the lost data (step S404), and the flow returns to stepS401. That is, in the case where the measurement section 602 hasdetected loss of video and/or audio data, for example, the communicationcontrol apparatus 610 performs processing for controlling retransmissionof data identical to the lost data. Operations performed by thecommunication control apparatus 610 in step S404 will be described withreference to FIG. 17.

FIG. 17 is a flowchart illustrating processing operations performed bythe communication control apparatus 610 according to the secondembodiment. The obtaining section 611 first obtains a temporal change inthe communication load (step 3501). The obtaining section 611 alsoobtains the number of transmission trials of a retransmission requestmessage (the number of request trials) (step S502). The obtainedtemporal change in the communication load and the number of requesttrials are inputted to the change section 612.

The change section 612 determines whether or not a duration during whichthe communication load keeps increasing (hereinafter referred to as an“increase duration”) exceeds a first threshold time (step S503). Here,if the increase duration exceeds the first threshold time (Yes in stepS503), the change section 612 increases the permitted time (step S504).That is, the change section 612 newly sets the permitted time that islonger than the current permitted time.

On the other hand, if the increase duration does not exceed the firstthreshold time (No in step S503), the change section 612 determineswhether or not a duration during which the communication load keepsdecreasing (hereinafter referred to as a “decrease duration”) exceeds asecond threshold time (step S505). Here, if the decrease durationexceeds the second threshold time (Yes in step 3505), the change section612 decreases the permitted time (step S506). That is, the changesection 612 newly sets the permitted time that is shorter than thecurrent permitted time. On the other hand, if the decrease duration doesnot exceed the second threshold time (No in step S505), the changesection 612 does not change the permitted time.

Next, the change section 612 determines the interval betweentransmissions that is appropriate for the permitted time so thatretransmitted data identical to lost data arrives at the receptiondevice 600 within the permitted time in the case where a retransmissionrequest message has been transmitted a number of times equal to thenumber of request trials (step S507). For example, the change section612 calculates the interval between transmissions that is appropriatefor the permitted time in accordance with expression (3) below.

Interval between Transmissions=(Permitted Time−RTT)/Number of RequestTrials  (3)

Here, RTT means round-trip time (RTT). That is, RTT is a round-tripcommunication delay time between the transmission device 500 and thereception device 600.

Next, the retransmission control section 613 controls transmission of aretransmission request message in accordance with the interval betweentransmissions determined in step S507 (step S508). That is, theretransmission control section 613 transmits, to the transmission device500 via the transmission section 603, a retransmission request messageat the determined interval between transmissions a number of times equalto the number of request trials (step S508).

Specific Example of Operations Performed in Communication System

Next, a specific example of operations performed in the communicationsystem according to this embodiment described above will be described.FIGS. 18A to 18C are diagrams for describing specific examples ofoperations performed in the communication system according to the secondembodiment. Specifically, FIG. 18A illustrates the interval betweentransmissions in the case where a first permitted time is set. FIG. 18Billustrates the interval between transmissions in the case where asecond permitted time that is longer than the first permitted time isset. FIG. 18C illustrates the interval between transmissions in the casewhere a third permitted time that is longer than the second permittedtime is set.

For example, in FIG. 18B, when loss of a data packet having the sequencenumber “1” occurs, the obtaining section 611 of the communicationcontrol apparatus 610 obtains a temporal change in the communicationload.

Here, if the decrease duration during which the communication load keepsdecreasing exceeds the second threshold time, the change section 612decreases the permitted time from the second permitted time to the firstpermitted time. Then, the change section 612 determines the intervalbetween transmissions on the basis of the first permitted time. As aresult, as illustrated in FIG. 18A, a retransmission request message istransmitted at the interval between transmissions shorter than that inFIG. 18B and therefore the communication band is effectively used.

On the other hand, if the increase duration during which thecommunication load keeps increasing exceeds the first threshold time,the change section 612 increases the permitted time from the secondpermitted time to the third permitted time. Then, the change section 612determines the interval between transmissions on the basis of the thirdpermitted time. As a result, as illustrated in FIG. 18C, aretransmission request message is transmitted at the interval betweentransmissions longer than that in FIG. 18B and therefore thecommunication load is reduced.

Effects

As described above, the communication control apparatus 610 according tothis embodiment is able to dynamically change the permitted time that isa time permitted to be used for recovery of data loss and the intervalbetween transmissions of a retransmission request message in accordancewith the communication load. Therefore, the communication controlapparatus 610 is able to balance suppression of increase in loss due tocommunication congestion with reduction in a reproduction delay. Thecommunication control apparatus 610 is able to efficiently recoverpacket loss relating to video and/or audio data occurring duringcommunication over the Internet while suppressing congestion caused bythe communication load, for example. In this case, the communicationcontrol apparatus 610 is able to reduce a reproduction delay inreproducing video and/or audio data, and is able to improve thereproduction quality of images and/or sounds.

The communication control apparatus 610 according to this embodiment isable to change the permitted time on the basis of the result ofcomparison between the duration during which the communication loadkeeps increasing or the duration during which the communication loadkeeps decreasing and the threshold. Therefore, the communication controlapparatus 610 is able to suppress frequent changes in the permitted timeand the interval between transmissions, and is able to attain stabledata reproduction and communication.

Other Embodiments

A communication control apparatus according to one aspect or a pluralityof aspects has been described with reference to embodiments, however,the present disclosure is not limited to the embodiments. Variousmodifications to the embodiments that may be conceived by those skilledin the art or an embodiment configured by combining constituent elementsin different embodiments may be included in the scope of one aspect or aplurality of aspects, without departing from the essence of the presentdisclosure.

Hereinafter, other embodiments will all be described.

A communication control apparatus may be configured by combiningconstituent elements of the communication control apparatus according tothe first embodiment described above and constituent elements of thecommunication control apparatus according to the second embodimentdescribed above.

Specifically, a communication control apparatus may include the firstobtaining section 311, the second obtaining section 312, the obtainingsection 611, the first determination section 314, the seconddetermination section 315 (315 a), the change section 612, and theretransmission control section 613, for example. With thisconfiguration, the communication control apparatus is able to controltransmission of a retransmission request message in accordance with thenumber of request trials determined as in the first embodiment and theinterval between transmissions dynamically changed as in the secondembodiment.

In the embodiments described above, an example of a case has beendescribed where data communication is communication performed over theInternet, however, the data communication need not be communicationperformed over the Internet. For example, the data communication may becommunication performed over a wired or wireless network, such as alocal area network or a wide area network. The data communication may bemobile communication used by a portable phone or the like. Furthermore,the data communication need not be packet communication.

In the embodiments described above, an example of a case has beendescribed where the communication system is a remote display system,however, the communication system need not be a remote display system.For example, the communication system may be a system in which textdata, image data, program data, or the like is transmitted from thefirst communication device to the second communication device.

In the embodiments described above, the communication control apparatusis integrated into the reception device, however, the communicationcontrol apparatus need not be integrated into the reception device. Thecommunication control apparatus may be configured as an apparatusprovided separately from the reception device. For example, thecommunication control apparatus may be integrated into a server that isconnected to a plurality of reception devices over the network. In sucha case, the communication control apparatus may control the plurality ofreception devices.

In the first embodiment described above, an example of a case has beendescribed where the first communication status and the secondcommunication status include the packet loss rate, however, the firstcommunication status and the second communication status need notinclude the packet loss rate. That is, the first communication statusand the second communication status may indirectly indicate thefrequency of occurrence of data loss. For example, the firstcommunication status and the second communication status may include thecongestion degree of the communication paths, the communication load,information about occurrence of communication failures, or the like.

In the first embodiment described above, the number of retransmissiontrials and the number of request trials are calculated so as to satisfyexpression (1) and expression (2) respectively, however, calculationneed not necessarily be performed in this way. The number ofretransmission trials and the number of request trials may be calculatedusing a function of the frequency of occurrence of loss. The number ofretransmission trials and the number of request trials may be determinedby referring to a table in which the number of retransmission trials andthe number of request trials that correspond to the frequency ofoccurrence of loss are registered.

In the first embodiment described above, a retransmission requestmessage contains information specifying the number of retransmissiontrials, however, a retransmission request message need not containinformation specifying the number of retransmission trials. For example,information specifying the number of retransmission trials may becommunicated in another message that is not a retransmission requestmessage.

In the first embodiment described above, the second communication statusis obtained from the transmission device, however, the secondcommunication status need not be obtained from the transmission device.For example, the second communication status may be obtained fromanother device that monitors the second data communication.

In the modified example of the first embodiment described above, anexample has been described where the number of retransmission trials,the first number of request trials, and the second number of requesttrials are sequentially determined, however, these numbers need not besequentially determined in this way. For example, the number of requesttrials (the second number of request trials) that is appropriate for thefirst communication status and the second communication status may bedirectly determined by referring to a table or a function.

In the second embodiment described above, the increase duration and thedecrease duration are used when changing the permitted time, however,these durations need not be used. For example, the permitted time may beincreased regardless of the increase duration in the case where thecommunication load is increasing, and the permitted time may bedecreased regardless of the decrease duration in the case where thecommunication load is decreasing.

In the second embodiment described above, the interval betweentransmissions is determined after the permitted time has been changed,on the basis of the permitted time obtained after such a change,however, the permitted time and the interval between transmissions neednot be determined in this way. For example, the permitted time may bedetermined after the interval between transmissions has been changed onthe basis of a temporal change in the communication load, on the basisof the interval between transmissions obtained after such a change. Theinterval between transmissions and the permitted time may be determinedat the same time by referring to a table in which a plurality ofcombinations of the interval between transmissions and the permittedtime are registered, for example.

Note that, in the embodiments described above, each constituent elementmay be configured by using dedicated hardware or by executing a softwareprogram applicable to each constituent element. Each constituent elementmay be implemented in such a manner that a program execution section,such as a central processing unit (CPU), a processor, or the like, readsand executes a software program recorded in a recording medium, such asa hard disk, a semiconductor memory, or the like. Here, software thatimplements the communication control apparatuses or the like accordingto the embodiments described above is a program as described below.

That is, the program causes a computer to perform a communicationcontrol method for controlling recovery of data loss during datacommunication from a first communication device to a secondcommunication device. The method includes a first obtaining step ofobtaining a first communication status indicating a frequency ofoccurrence of data loss during first data communication from the firstcommunication device to the second communication device, a secondobtaining step of obtaining a second communication status indicating afrequency of occurrence of data loss during second data communicationfrom the second communication device to the first communication device,and a control step of controlling transmission processing oftransmitting, from the second communication device to the firstcommunication device, a retransmission request message that requestsretransmission of data identical to lost data during the first datacommunication, in accordance with the first communication status and thesecond communication status.

INDUSTRIAL APPLICABILITY

The communication control apparatus of the present disclosure is able toimprove the reproduction quality of images and/or sounds and thereforeis usable in a video conference system or the like in which video and/oraudio data are transmitted and received.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims the benefit of Japanese PatentApplication No. 2013-187981 filed on Sep. 11, 2013. The entiredisclosure of the above-identified application, including thespecification, drawings and claims, is incorporated herein by referencein its entirety.

What is claimed is:
 1. A communication control apparatus for controllingrecovery of data loss during data communication from a firstcommunication device to a second communication device, the communicationcontrol apparatus comprising: an obtaining section configured to obtaina temporal change in a communication load between the firstcommunication device and the second communication device; a changesection configured to dynamically change a permitted time and aninterval between transmissions on the basis of the temporal change inthe communication load, the permitted time being a time that ispermitted to be used by the second communication device for recovery ofdata loss, the interval between transmissions being an interval betweentransmissions of a retransmission request message that requestsretransmission of data identical to lost data in a case where theretransmission request message is repeatedly transmitted from the secondcommunication device to the first communication device; and aretransmission control section configured to control transmission of theretransmission request message in accordance with the interval betweentransmissions.
 2. The communication control apparatus according to claim1, wherein the change section dynamically changes the permitted time onthe basis of the temporal change in the communication load, anddetermines the interval between transmissions that is appropriate forthe permitted time so that the retransmitted data identical to the lostdata arrives at the second communication device within the permittedtime in a case where the retransmission request message has beentransmitted a number of times equal to a number of request trials. 3.The communication control apparatus according to claim 2, wherein thechange section increases the permitted time in a case where thecommunication load is increasing, and decreases the permitted time in acase where the communication load is decreasing.
 4. The communicationcontrol apparatus according to claim 3, wherein the change sectionincreases the permitted time in a case where a duration during which thecommunication load keeps increasing exceeds a first threshold time, anddecreases the permitted time in a case where a duration during which thecommunication load keeps decreasing exceeds a second threshold time. 5.The communication control apparatus according to claim 1, wherein theobtaining section estimates a temporal change in the communication loadin accordance with at least one of temporal changes in a loss frequency,a delay time, and traffic in the first data communication.
 6. Thecommunication control apparatus according to claim 1, wherein theobtaining section obtains a temporal change in the communication loadfrom outside the communication control apparatus.